By Craig DiLouie
Image courtesy of the Energy Center of Wisconsin.Daylight harvesting control, or the practice of using light sensors to automatically reduce electric light in a space when sufficient daylight is present, has been demonstrated to produce significant energy cost savings in buildings. As a proven energy-saving strategy, it has been implemented into many sustainable building projects. It was also incorporated into ASHRAE/IES 90.1-2010 and IECC 2009/2012, the major energy standards. Daylight harvesting should soon become a staple in new construction.
For a daylight harvesting control system to satisfy the owner, achieve the design intent and gain occupant acceptance, a chain of proficiency must be realized. The equipment must operate properly, the designer must articulate the design intent and properly place and orient devices, and the contractor must properly install them. Best practice encourages these proficiencies be formalized within The Commissioning Process, in which a Commissioning Authority, executing a Commissioning Plan approved by the owner, checks each step to ensure that the owner is delivered a fully functioning lighting control system that satisfies the design intent.
With a grant from the Minnesota Department of Commerce, Division of Energy Resources, the Energy Center of Wisconsin (ECW) put this notion to the test in a study of 20 office and public assembly spaces in Minnesota and Wisconsin, collecting sub-hourly measurements of light levels, lighting power, and heating/cooling data over six months (January 13, 2012 through July 10, 2012) for 1) controls as they were found and 2) controls after the system was recommissioned to realize operation as close to the ideal as possible.
Collected data included current of controlled lighting circuits, critical workplane light levels, open-loop light levels, HVAC supply air temperature, voltage and power factor, and window treatment position. The results were published in “Commissioning for Optimal Savings from Daylight Controls,” published in February 2013.
The researchers concluded:
1. “First, when installed, commissioned and operated to perform as designed, daylighting controls can be an economically attractive solution for some building owners and managers. The systems we monitored typically exhibited substantial energy savings.”
2. “Secondly, we have identified a significant amount of savings being ‘left on the table’ in systems that are designed for substantial energy savings but fall considerably short of optimal performance.”
3. “The demonstrated savings indicates that there is value to be captured in the commissioning process for building projects. As a result, the real opportunity here comes from contractors, commissioning agents and utility program implementers to demonstrate this value to building designers and owners and ensure that these steps are completed.”
4. “Finally, there is a substantial number of daylighting control systems already implemented that have room for improvement due to incomplete execution.”
The lessons learned in this study go beyond daylight harvesting control, posing implications for all lighting control systems, particularly as they become more sophisticated to satisfy the latest generation of energy codes and standards. The Commissioning Process, properly executed, can ensure delivery of control solutions that satisfy the design intent and owner’s operational needs. Elements of this process are now featured in ASHRAE/IES 90.1-2010 and IECC 2012, and are expected to become staple activities in construction.
Courtesy of Lighting Controls Association.
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